Courts won't generally honor contracts made under duress. If the coerced party is in breach, then they cannot be held liable for the terms of the contract. Treaties written at the close of a decisive war are fairly isomorphic to a contract written under duress, yet the defeated sovereignty lacks the same redress as private individuals.
Furthermore, the coercive agency, supposing they retain a wide disparity in BATNA, faces no constraints on arbitrarily altering the terms of the treaty. Witness Senate Bill 2109. It reads kind of choppy, but it seems to be aimed at addressing relative scarcity issues with regard to water rights in the arid American Southwest. There's no good price mechanism to sort the big ol' bag of multiple, conflicting property rights among the several American Indian Tribes. McCain et al therefore revisit the treaty clubhouse to "renegotiate". "Renegotiate", that is, in much the same way France, Britain and the United States negotiated with Germany at Versailles in 1919.
Knowing that it's the case that the Federal authority retains more or less unilateral power to rewrite the terms of a tribal treaty (subject, naturally to the standard Public Choice constraints, here mostly the MVT), can we consider treaties between Washington DC and the Indian Nations to be morally legitimate? Are they even really treaties at all or merely soft promises of restraint? Is a disparity in BATNA relevant to the retention of the force of law (and I use the term "law" here in the emergent, Hayekian sense as opposed to the Hobbesian, civil legislation use of the word), especially as concerns enforcement? Is it important that property rights are fragmented, absent or ill-defined? How could the tribes get out of this pickle?